Advances in semi-conductor processing and logic design have permitted an increase in the amount of logic that may be present on integrated circuit devices. As a result, computer system configurations have evolved from a single or multiple integrated circuits in a system to multiple hardware threads, multiple cores, multiple devices, and/or complete systems on individual integrated circuits. Additionally, as the density of integrated circuits has grown, the power requirements for computing systems (from embedded systems to servers) have also escalated. Furthermore, software inefficiencies, and its requirements of hardware, have also caused an increase in computing device energy consumption. In fact, some studies indicate that computing devices consume a sizeable percentage of the entire electricity supply for a country, such as the United States of America. As a result, there is a vital need for energy efficiency and conservation associated with integrated circuits. These needs will increase as servers, desktop computers, notebooks, ultrabooks, tablets, mobile phones, processors, embedded systems, etc. become even more prevalent (from inclusion in the typical computer, automobiles, and televisions to biotechnology).
As the trend toward advanced microprocessors, e.g. central processing units (CPUs) or “processors”, with more transistors and higher frequencies continues to grow, computer designers and manufacturers are often faced with corresponding increases in power and energy consumption. Particularly in computing devices, processor power consumption can lead to overheating, which may negatively affect performance, waste energy, damage the environment, and can significantly reduce battery life. In addition, because batteries typically have a limited capacity, running the processor of a mobile device more than necessary could drain the capacity more quickly than desired. Moreover, processor power consumption can be more efficiently controlled to increase energy efficiency and conservation associated with integrated circuits (e.g., the processor).
Thus, power consumption continues to be an important issue for computing devices including desktop computers, servers, laptop computers, wireless handsets, cell phones, tablet computers, personal digital assistants, etc. In today's computing devices, for example, to address power dissipation concerns, certain components may be placed into lower power sleep states based on reduced activity or demand.
For one approach, an operating system may support a built-in power management software interface such as Advanced Configuration and Power Interface (ACPI) specification (for example, ACPI Specification, Revision 4.0a, published on Apr. 5, 2010 . . . Rev. 3.0, Sep. 2, 2004; Rev. 2.0c, Aug. 25, 2003; Rev. 2.0, Jul. 27, 2000, etc.). ACPI describes a power management policy including various “C states” that may be supported by processors and/or chipsets. For this policy, C0 is defined as the Run Time state in which the processor operates at high voltage and high frequency. C1 is defined as the Auto HALT state in which the core clock is stopped internally. C2 is defined as the Stop Clock state in which the core clock is stopped externally. C3 is defined as a Deep Sleep state in which all processor clocks are shut down, and C4 is defined as a Deeper Sleep state in which all processor clocks are stopped and the processor voltage is reduced to a lower data retention point. C5 is a Deeper Sleep state in which the processor voltage is reduced to near zero, but some components remain powered so the computer can “wake” from input from the keyboard, clock, modem, LAN, or USB device. C6 is a Deeper Sleep state known as the zero, near zero, or voltage sleep state.